The last time he admitted to cheating was when he was 16

And in a non-FIDE (online) event.

If he was caught in a FIDE event then of course a ban should be permanent, much like athletics.

Imagine if they did that at the FAANG. There would be no more recruits. What percentage of all technical interviews at FAANG involve the candidate googling the answer in a way that the interviewer didn't know about?

My guess? Over 30%

At least pre-pandemic, that would be hard to do at the last stage (on-sites). You're generally in a room with one or more people and often whiteboarding rather than using a laptop. In the stages leading up to on-sites, in many cases, you're actually allowed to use reference materials like the official documentation -- which might contain examples -- because the interviewers don't necessarily expect you to have the entire standard library of the language you're using memorized. I've certainly Googled stuff during remote interviews myself, but I disclose that I'm doing that and explain what I'm searching for.